High Quality Content by WIKIPEDIA articles! A mucolytic agent or expectorant is any agent which dissolves thick mucus and is usually used to help relieve respiratory difficulties. It does so by hydrolyzing glycosaminoglycans, tending to break down/lower the viscosity of mucin-containing body secretions/components. The viscosity of mucous secretions in the lungs is dependent upon the concentrations of mucoprotein, the presence of disulfide bonds between these macromolecules and DNA.